Cancer is a leading cause of death in the United States. Various types of therapies have been used to treat cancer. For example, surgical methods are used to remove cancerous or dead tissue. Radiotherapy, which works by shrinking solid tumors, and chemotherapy, which kills rapidly dividing cells, are used as cancer therapies.
In 1971, Folkman proposed that anti-angiogenesis might be an effective anticancer strategy. Folkman, N. Engl. J. Med. 285, 1182-1186 (1971). Angiogenesis is the development of new vasculature from preexisting blood vessels and/or circulating endothelial stem cells (see, e.g., Ferrara & Alitalo, Nature Medicine 5(12)1359-1364 (1999)). Angiogenesis is a cascade of process consisting of 1) degradation of the extracellular matrix of a local venue after the release of protease, 2) proliferation of capillary endothelial cells, and 3) migration of capillary tubules toward the angiogenic stimulus. Ferrara et al. Endocrine Rev. 13:18-32 (1992).
The growth of new blood vessels is a prerequisite during normal physiological processes of embryonic and postnatal development, e.g., embryogenesis, wound healing and menstruation. See, e.g., Folkman and Klagsbrun Science 235:442-447 (1987). Such proliferation of new blood vessels from pre-existing capillaries additionally plays a key role in the pathological development of a variety of disorders, including but not limited to, e.g., tumors, proliferative retinopathies, age-related macular degeneration, psoriasis, inflammation, diabetes, and rheumatoid arthritis (RA). See, e.g., Ferrara, Recent Prog. Horm. Res. 55:15-35 (2000), discussion 35-6.
In view of the remarkable physiological and pathological importance of angiogenesis, much work has been dedicated to the elucidation of the factors capable of regulating this process. It is suggested that the angiogenesis process is regulated by a balance between pro- and anti-angiogenic molecules, and is derailed in various diseases, especially cancer. See, e.g., Carmeliet and Jain Nature 407:249-257 (2000).
For example, angiogenesis is dependent on secreted factors like Vascular endothelial growth factor-A (VEGF, also known as vascular permeability factor (VPF)) and fibroblast growth factor (FGF). See, e.g., Ferrara and Davis-Smyth Endocrine Rev. 18:4-25 (1997); and, Ferrara J. Mol. Med. 77:527-543 (1999). In addition to being an angiogenic factor in angiogenesis and vasculogenesis, VEGF, as a pleiotropic growth factor, exhibits multiple biological effects in other physiological processes, such as endothelial cell survival, vessel permeability and vasodilation, monocyte chemotaxis and calcium influx. Ferrara and Davis-Smyth (1997), supra. Moreover, studies have reported mitogenic effects of VEGF on a few non-endothelial cell types, such as retinal pigment epithelial cells, pancreatic duct cells and Schwann cells. See, e.g., Guerrin et al. J. Cell Physiol. 164:385-394 (1995); Oberg-Welsh et al. Mol. Cell. Endocrinol. 126:125-132 (1997); and, Sondell et al. J. Neurosci. 19:5731-5740 (1999).
VEGF belongs to a gene family that includes placental growth factor (PIGF), VEGF-B, VEGF-C, VEGF-D and VEGF-E. These ligands bind to and ligate to tyrosine kinase receptors expressed on endothelial cells. For example, VEGF tyrosine kinase receptor family includes Flt1 (VEGF-R1) (which binds ligands VEGF, VEGF-B and PIGF), Flk1/KDR (VEGF-R2) (which binds VEGF, VEGF-C, VEGF-D, and, VEGF-E), and Flt4 (VEGF-R3) (which binds VEGF-C and VEGF-D). See, e.g., Ferrara et al., Nature Medicine 9(6):669-676 (2003); and, Robinson & Stringer, Journal of Cell Science, 14(5):853-65 (2001).
The Angiopoietins are another group of growth factors for the vascular endothelium. See, e.g., Davis et al., Cell, 87:1161-1169 (1996); Suri et al., Cell, 87:1171-1180 (1996); Maisonpierre et al. Science 277:55-60 (1997); and Valenzuela et al., Proc. Natl. Acad. Sci. USA 96:1904-1909 (1999). Angiopoietins appear to work in a complementary and coordinate fashion with VEGF, where VEGF acts in vascular development while angiopoietins most likely act by modulating remodeling, maturation and stabilization of the vasculature. See, e.g., Holash et al., Oncogene 18:5356-5362 (1999). Angiopoietin 1, Angiopoietin 2, Angiopoietin 3 and Angiopoietin 4 bind to tyrosine kinase Tie2 (also know as Tek) receptors, which are receptors found on endothelial cells. See, e.g., Ward & Dumont, Seminars in Cell & Developmental Biology, 13:19-27 (2002). There is also a Tie1 orphan receptor.
Angiogenesis not only depends on growth factors, but is also influenced by cell adhesion molecules (CAMs), including integrins, binding to their ligands present within the extracellular matrix. See, e.g., Ferrara & Alitalo, Nature Medicine 5(12)1359-1364 (1999); and, Carmeliet, Nature Medicine, 6(3):389-395 (2000). Integrins facilitate cellular adhesion to and migration on the extracellular matrix proteins found in intercellular spaces and basement membranes. The integrin family of cell adhesion proteins is composed of at least 18α and 8β subunits that are expressed in at least 22αβ heterodimeric combinations. See, e.g., Byzova et al., Mol. Cell., 6(4):851-860 (2000); and, Hood and Cheresh, Nature Reviews, 2:91-99 (2002). Among these, at least six (αvβ3, αvβ5, α5β1, α2β1, αvβ1 and α1β1) of the combinations have been implicated in angiogenesis (see, e.g., Hynes and Bader, Thromb. Haemost., 78(1):83-87 (1997); and, Hynes et al., Braz. J. Med. Biol. Res., 32(5):501-510 (1999)). Inactivation of various genes encoding specific adhesion receptors or administration of blocking antibodies in animal models had profound effects on the angiogenic response of endothelial cells. See, e.g., Elicieri and Cheresh, Mol. Med., 4:741-750 (1998).
These molecules have been targets for cancer therapies. For example, recognition of VEGF as a primary regulator of angiogenesis in pathological conditions has led to numerous attempts to block VEGF activities. Inhibitory anti-VEGF receptor antibodies, soluble receptor constructs, antisense strategies, RNA aptamers against VEGF and low molecular weight VEGF receptor tyrosine kinase (RTK) inhibitors have all been proposed for use in interfering with VEGF signaling. See, e.g., Siemeister et al. Cancer Metastasis Rev. 17:241-248 (1998). Anti-VEGF neutralizing antibodies have been shown to suppress the growth of a variety of human tumor cell lines in nude mice (Kim et al. Nature 362:841-844 (1993); Warren et al. J. Clin. Invest. 95:1789-1797 (1995); Borgström et al. Cancer Res. 56:4032-4039 (1996); and Melnyk et al. Cancer Res. 56:921-924 (1996)) and also inhibit intraocular angiogenesis in models of ischemic retinal disorders (Adamis et al. Arch. Ophthalmol. 114:66-71 (1996)). Indeed, a humanized anti-VEGF antibody, bevacizumab (AVASTIN®, Genentech) has been approved by the US FDA as a first-line therapy for metastic colorectal cancer. See, e.g., Ferrara et al., Nature Reviews Drug Discovery, 3:391-400 (2004).
However, current methods of cancer treatment are not always optimal. Often, a single type of therapy cannot completely suppress a pathological condition. For example, surgical procedures often cannot remove all the cancerous growth. Other cancer treatments, such as chemotherapy, have numerous side effects, and/or therapy becomes ineffective, e.g., because the cancer develops a resistance to the drug or treatment. Inhibition of VEGF or a VEGR receptor, or of the Tie2 receptor system sometimes did not completely suppress tumor growth. See, e.g., Gerber et al., Cancer Research, 60:6253-6258 (2000); Ferrara et al., Nature Reviews: Drug Discovery, 3:391-400 (2004); Millauer et al., Nature 367, 576-579 (1994); Kim et al., Nature 362: 841-844 (1993); Millauer et al., Cancer Res. 56:1615-1620 (1996); Goldman et al., Proc. Natl. Acad. Sci. USA 95:8795-8800 (1998); Asano et al., Cancer Research, 55:5296-5301 (1995); Warren et al., J. Clin. Invest., 95:1789-1797 (1995); Fong et al., Cancer Res. 59:99-106 (1999); Wedge et al., Cancer Res. 60:970-975 (2000); Wood et al. Cancer Res. 60:2178-2189 (2000); Siemeister et al., Cancer Res. 59:3185-3191 (1999); Lin et al., J. Clin. Invest. 103:159-165 (1999); Lin et al., Proc. Natl. Acad. Sci. USA 95:8829-8834 (1998); and, Siemeister et al., Cancer Res. 59, 3185-3191, (1999).
Thus, there is an urgent need for new and more effective therapies for regulating cancers. The invention addresses these and other needs, as will be apparent upon review of the following disclosure.